ptsname(3)                 Library Functions Manual                 ptsname(3)

NAME
       ptsname, ptsname_r - get the name of the slave pseudoterminal

LIBRARY
       Standard C library (libc, -lc)

SYNOPSIS
       #include <stdlib.h>

       char *ptsname(int fd);
       int ptsname_r(size_t size;
                     int fd, char buf[size], size_t size);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       ptsname():
           Since glibc 2.24:
               _XOPEN_SOURCE >= 500
           glibc 2.23 and earlier:
               _XOPEN_SOURCE

       ptsname_r():
           _GNU_SOURCE

DESCRIPTION
       The ptsname() function returns the name of the slave pseudoterminal
       device corresponding to the master referred to by the file descriptor
       fd.

       The ptsname_r() function is the reentrant equivalent of ptsname().  It
       returns the name of the slave pseudoterminal device as a null-
       terminated string in the buffer pointed to by buf.  The size argument
       specifies the number of bytes available in buf.

RETURN VALUE
       On success, ptsname() returns a pointer to a string in static storage
       which will be overwritten by subsequent calls.  This pointer must not
       be freed.  On failure, NULL is returned.

       On success, ptsname_r() returns 0.  On failure, an error number is
       returned to indicate the error.

ERRORS
       EINVAL (ptsname_r() only) buf is NULL.  (This error is returned only
              for glibc 2.25 and earlier.)

       ENOTTY fd does not refer to a pseudoterminal master device.

       ERANGE (ptsname_r() only) buf is too small.

ATTRIBUTES
       For an explanation of the terms used in this section, see
       attributes(7).

       +-----------------------------+---------------+------------------------+
       |Interface                    | Attribute     | Value                  |
       +-----------------------------+---------------+------------------------+
       |ptsname ()                   | Thread safety | MT-Unsafe race:ptsname |
       +-----------------------------+---------------+------------------------+
       |ptsname_r ()                 | Thread safety | MT-Safe                |
       +-----------------------------+---------------+------------------------+
VERSIONS
       A version of ptsname_r() is documented on Tru64, HP-UX, and FreeBSD,
       but on those implementations, -1 is returned on error, with errno set
       to indicate the error.  Avoid using this function in portable programs.

STANDARDS
       ptsname():
              POSIX.1-2008.

       ptsname_r():
              POSIX.1-2024.

HISTORY
       ptsname():
              POSIX.1-2001.  glibc 2.1.

       ptsname() is part of the UNIX 98 pseudoterminal support (see pts(4)).

       ptsname_r():
              GNU.

SEE ALSO
       grantpt(3), posix_openpt(3), ttyname(3), unlockpt(3), pts(4), pty(7)

Linux man-pages 6.17              2025-10-29                        ptsname(3)